Agenda - Council - 01/08/2019 - Laserfiche WebLink

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Brookview Estates Reconstruction Ramsey, Minnesota NTI Project No. 18.MSP06855.000 The Contractor should be aware that the silty subgrade soils will be moisture -sensitive, and protecting them from inclement weather will aid in maintaining stability. The stripping of the existing pavement and aggregate base course should occur immediately prior to subgrade preparation and base aggregate installation to minimize weather -induced instability. Prior to installing the aggregate base, the existing subgrade should be scarified and re -compacted to a depth of at least 12 inches. A proof roll test should then be performed to determine soft or unstable subgrade areas. The proof roll should be performed with a tandem axle dump truck loaded to gross capacity (at least 20 tons). Acceptance criteria of the proof roll shall be limited to rut formation no more than one inch depth (front or rear axles) and no pumping (rolling) observed during the visual inspection. Proof roll tests should be observed by an experienced technician or geotechnical engineer prior to placement of the aggregate base course to verify the subgrade will provide adequate pavement support. If rutting or localized unstable subgrade areas are observed, those areas should be subcut, moisture - conditioned, and re -compacted or removed to a stable depth. If imported fill is required in paved areas, it should consist of debris -free, non -organic, mineral soil similar in composition to the subgrade soils encountered in the surrounding areas. If sand is imported into areas that are underlain by relatively impervious fine grained soils, the sand layer must be drained with drain tile in order to prevent frost heave from water trapped within the imported sand layer during freezing temperatures. Individual lifts of engineered fill should be tempered for moisture content, placed, and compacted as noted in the "Placement and Compaction of Engineered Fill" section in Appendix B of this report. For a 20-year design pavement life, Tables 4 presents our thickness recommendations for flexible (bituminous) pavement. These recommendations were based upon the encountered subgrade conditions, estimated R-value of 30 for the existing subgrade soils, the assumed AADT volumes, and the City of Ramsey's typical pavement section for the respective project area. Pavement Section Table 4: Flexible Pavement Thickness Design' Interstate Area — Residential Area Calculated Required City's Typical Pavement Section2 Pavement Section3 Bituminous Wear Course (inches) 2 1.5 Bituminous Base Course (inches) 2 2 Class 5 or 7 Aggregate Base (inches) 4 4 1. Assumed AADT volume of 600 and an average R-value of 30. 2. Assumed a minimum of 12 inches of engineered subgrade. 3. The subgrade appeared to be less firm at SB-2 and SB-7 (locations closest to the Rum River). Consideration could be made to using the City's standard section in locations north of SB-2 and west of SB-6. Page 4 of 7